Method and device for regulating a headbox

Abstract: The invention concerns a method and a device in the regulation of the headbox of a paper machine/board machine, in which method additional flows are introduced into the pulp suspension at different points across the width of the headbox, the concentration of said additional flow differing from the average concentration of the pulp suspension. The additional flows (Q 2.1 ,Q 2.2 ...Q 2.n ) are introduced through additional-flow pipes (26a₁,26a₂...26a n ) to the vicinity of the inlet opening (C₁,C₂...) of the turbulence tube (29a₁,29a₂...) of the turbulence generator (20). In the method, the grammage profile of the web in the direction of width of the web is regulated by, in the headbox, adjusting the distance of the end of the additional-flow pipe/pipes (26a₁,26a₂...) from the turbulence generator (20), whereby the amount of the additional flow (Q 2.1 , Q 2.2 ...) entering into the additional-flow pipe (26a₁,26a₂...) and, at the same time, the amount of the pulp suspension flow (Q 1.1 , Q 1.2 ...) are affected, whereby the combined flow (Q 3.1 , Q 3.2 ...), as a sum flow into the turbulence generator (20), is regulated.

Description: The invention concerns a method and a device in the regulation of the headbox of a paper/board machine. As is known from the prior art, the discharge flow of the pulp suspension out of the headbox must be of uniform velocity in the transverse direction of the paper machine. A transverse flow, which produces distortion of the fibre orientation, affects the quality factors of the paper produced, such as anisotropy of strength and stretch. The level and variation of anisotropy in the transverse direction also affect the printing properties of the paper. In particular, it is an important requirement that the main axes of the directional distribution, i.e. orientation, of the fibre mesh in the paper coincide with the directions of the main axes of the paper and that the orientation is symmetric in relation to these axes. At the edges of the pulp-flow duct in the headbox, a smaller amount of pulp flows. This edge effect produces a very strong linear distortion in the fibre-orientation profile. Profile faults in the turbulence generator of the headbox usually produce a non-linear distortion in the fibre-orientation profile inside the lateral areas of the flow ducts. Attempts are made to compensate for an unevenness of the grammage profile arising from the drying-shrinkage of paper by means of a crown formation of the slice, so that the slice is thicker in the middle of the pulp jet. When the paper web is dried, it shrinks in the middle area of the web to a lower extent than in the lateral areas, the shrinkage being, as a rule, in the middle about 4 % and in the lateral areas about 5...6 %. Said shrinkage profile produces a corresponding change in the transverse grammage profile of the web so that, owing to the shrinkage, the dry grammage profile of a web whose transverse grammage profile was uniform after the press is changed during the drying so that, in both of the lateral areas of the web, the grammage is slightly higher than in the middle area. As is known from the prior art, said grammage profile has been regulated by means of the profile bar so that the profile bar of the headbox is kept more open in the middle area than in the lateral areas. By means of said arrangement, the pulp suspension is forced to move towards the middle area of the web. Said circumstance further affects the alignment of the fibre orientation. The main axes of the directional distribution, i.e. orientation, of the fibre mesh should coincide with the directions of the main axes of the paper, and the orientation should be symmetric in relation to these axes. In said regulation of the profile bar, a change in the orientation is produced as the pulp suspension flow receives components in the transverse direction. Regulation of the lip of the headbox also produces a change in the transverse flows of the pulp jet even though the objective of the regulation is exclusively to affect the grammage profile, i.e. the thickness profile of the pulp suspension layer that is fed. Thus, the transverse flows have a direct relationship with the distribution of the fibre orientation. From the prior art, solutions of equipment are known separately by whose means attempts are made to regulate the fibre orientation, and solutions of equipment are known separately by whose means attempts are made to regulate the grammage profile of the web. However, when the grammage profile is regulated in a prior-art solution by means of the profile bar, the fibre orientation in the web is unavoidably also affected at the same time. From the prior art, a method is known in the headbox of the paper machine for the control of the distortion of the fibre orientation in the paper web. In the method, medium flows are passed into lateral passages placed at the level of the turbulence generator of the headbox, and, by regulating the magnitudes and the mutual proportions of said flows, the transverse flows of the pulp suspension are affected, and thereby the distortion of the fibre orientation is regulated. By means of the flows introduced into the lateral passages, a transverse flow velocity is produced which compensates for the distortion of the fibre orientation. On the other hand, from the applicant's US Patent Specification No . 5 022 965 of earlier date, a method is known in the headbox of a paper machine for the control of the distribution of the fibre orientation of the paper web in the transverse direction of the machine, in which method the transverse velocity component of the discharge jet is regulated by aligning the turbulence tube of the turbulence generator. By means of the above prior-art methods for the control of the fibre orientation in the paper web, it is, as a rule, possible to control the linear distortion profiles only. The prior-art methods are suitable for the control of the fibre orientation, but, when they are used, commonly even a large non-linear residual fault remains in comparison with an even distribution of the orientation. The prior-art methods are well suitable for basic regulation of the distortion of the orientation. However, by means of the prior-art methods, it is not possible to regulate individual faults, which may occur in the orientation in the middle area of the web and which arise, e.g., from defects in the pipe system of the turbulence generator. A number of methods are also known for the regulation of the profile bar, in which cases, while the grammage profile is measured, the position of the profile bar in the headbox of the paper machine is changed and, by means of the profile bar, the thickness of the pulp suspension discharged onto the wire, and thereby, the grammage of the paper web are affected. In the way described above, said regulation, however, produces faults in the orientation, because, by means of the regulation, the flow is throttled on one hand, whereby components of transverse velocity are produced in the flow. In the present application, a method of an entirely novel type is described, by whose means it is possible to control both the fibre-orientation profiles and the grammage-orientation profiles of the paper web across the width of the paper web. The method according to the invention has the features of claim 1. DE-3 741 603 discloses a method of regulating a headbox for controlling the grammage profile a web, the headbox comprising in the flow direction of the pulp suspension an inlet header, a distribution mainfold, an intermediate chamber, a turbulence generator comprising a plurality of tubes, and a discharge duct, in which method additional flows are introduced into the pulp suspension at different points across the width of the headbox, the concentration of said additional flows differing from the average concentration of the pulp suspension fed into the intermediate chamber, the additional flows being introduced through additional-flow pipes in the vicinity of the inlet openings of the tubes of the turbulence generator in the intermediate chamber, and in which method the grammage profile of the web in the width direction thereof is regulated by regulating the quantity of the additional flows in the additional-flow pipes. The preamble of claim 8 is based on DE-3 741 603, and the headbox according to the invention has the features of the characterizing part of claim 8. In the solution of the present invention, the grammage profile is affected by into the pulp flow adding a component flow, whose concentration differs from the average concentration of the pulp flow. Thus, into the main pulp flow, it is possible to add, for example, water alone, i.e. 0-water, or a diluted pulp suspension, whose concentration differs from the concentration of the main pulp flow. In the prior-art solution, the grammage profile was changed by acting upon the thickness of the discharge jet by means of the profile bar. In the solution of equipment of the present invention, a profile bar is not needed necessarily. In the solution in accordance with the invention, the headbox comprises separate zones across the width of the headbox, into which zones it is possible to feed an additional flow, whose consistency has been regulated to the desired level and by means of which additional flow a fault in the grammage profile occurring in a certain width position of the web is corrected. Thus, into a certain position of width in the headbox, it is possible to introduce a pulp suspension thicker than average or a pulp suspension more dilute than average, such as 0-water, depending on the measured grammage-profile error, so as to correct said error. However, it is essential in the regulation of the grammage profile that the flow quantity of the sum flow Q 3 = Q 1 + Q 2 is kept invariable and that, thus, in the regulation of the consistency, no changes are produced in the overall flow-velocity profile of the pulp suspension. Thus, by means of the additional flow Q 2 in the regulation of consistency, exclusively the consistency of the pulp suspension at a certain position of width is affected. Thus, by means of the flow Q 2 , any faults occurring in the grammage profile are corrected. In the method in accordance with the invention, the fibre orientation is regulated by regulating the flow quantity Q 3.1 ,Q 3.2 ...Q 3.n . Thus, when it is desirable to correct the fibre-orientation profile, the flow-velocity profile coming out of the system of tubes of the turbulence generator is affected locally in the direction of width of the web, and the flow quantity is increased or, if necessary, reduced locally at a certain position of width of the web. In this way, it is possible to act upon any local faults occurring in the fibre orientation. The headbox in accordance with the invention comprises, proceeding in the flow direction F of the pulp suspension, an inlet header, a distribution manifold and an equalizing chamber, a turbulence generator, and a discharge duct. The discharge duct is defined by a stationary lower-lip wall and by an upper-lip wall pivoting around a horizontal articulated joint. The upper-lip beam and, along with it, the upper-lip wall are arranged to be pivoted around said articulated joint by means of a screw gear. The profile bar that defines the slice from above is regulated by means of a series of adjusting spindles and a series of adjusting gears. However, in the solution of equipment in accordance with the invention, a separate profile bar is not needed necessarily. According to the invention, the headbox comprises pipes for the introduction of the additional flow, which pipes are fitted so that their ends are placed at a distance from the inlet openings of the turbulence tubes in the turbulence generator. The pipes are fitted to be displaceable, and through them an additional flow Q 2 is introduced, the concentration of said additional flow differing from the average concentration of the pulp suspension. Advantageously, the additional flow Q 2 is merely water free from pulp fibres, i.e. so-called 0-water. In the solution in accordance with the invention, the pipes are passed through the end wall in the intermediate chamber, and, at one end, they comprise an opening in the mantle face of the pipe, which opening is opened into the additional-flow distribution chamber for the additional flow Q 2 . Thus, the additional flow is introduced from a separate distribution chamber into the pipes and through them into connection with the inlet end of the turbulence generator. By regulating the position of the pipes in relation to the end of the turbulence generator, the throttle of the flow of the pulp suspension in the intermediate chamber from the intermediate chamber into the tubes in the turbulence generator is also regulated. There may be several pipes in the vertical direction, and in the direction of width the pipes are placed with a certain spacing across the entire width of the headbox. Thus, an additional flow Q 2.1 ,Q 2.2 , Q 2.3 ...Q 2.n is passed into a certain and desired position of width of the headbox into a certain zone so as to regulate the consistency of the pulp suspension locally. The additional flow Q 2.1 ,Q 2.2 ,Q 2.3 ...Q 2.n and the pulp flow Q 1.1 ,Q 1.2 ,Q 1.3 ...Q 1.n are combined into the flow Q 3.1 ,Q 3.2 ,Q 3.3 ...Q 3.n in the turbulence tube in the turbulence generator. In the solution in accordance with the invention, the end of the set of ducts for the additional flow is connected with an actuator, which displaces the additional-flow pipe towards the turbulence generator or apart from same. By means of the actuator, it is possible to move either one pipe or a separate vertical group of pipes. In a corresponding way, the pipes may have been installed together as groups in the direction of width of the machine, in which case the moving of the pipes may take place under group control or by moving each pipe individually. The additional flow into the additional-flow pipe out of the additional-flow distribution chamber is regulated separately. For said regulation, there is a separate bushing, the additional-flow pipe and the flow opening A provided in its mantle face being displaceable into different positions in relation to the bushing, whereby the covering of the opening A is altered. The bushing is also fitted to be displaceable in the opening in the end wall of the additional-flow distribution chamber. The bushing surrounds the additional-flow pipe. The invention will be described below with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawings, the invention being, yet, not supposed to be confined to said embodiments alone. Figure 1 is a vertical sectional view of a headbox of a paper machine in accordance with the invention. Figure 2 shows the headbox as viewed in the direction of the arrow K 1 in Fig. 1. Figure 3 is a separate illustration of the fitting of an additional-flow pipe in connection with the headbox. Figure 4 shows a second end construction of the turbulence generator and an additional-flow pipe in connection with said construction. Figure 5 illustrates the regulation of the additional flow by means of a bushing. Figure 6 shows a second embodiment of the coupling between the bushing and the additional-flow pipe. Figures 7A to 7C show different embodiments of the regulation. Fig. 1 shows the headbox in connection with a twin-wire former. Of the former, in Fig. 1, the breast rolls 10 and 11 and the forming wires 12 and 13 that run over said breast rolls are shown, said wires defining the forming gap G between them. Out of the discharge duct 14 of the headbox, a pulp suspension jet is fed through the slice 16 defined by the profile bar 15 into the forming gap G defined by the wires 12 and 13. Proceeding in the flow direction F of the pulp suspension, the headbox comprises an inlet header 17, a distribution manifold 18, an intermediate chamber 19, a turbulence generator 20, and a discharge duct 14. The discharge duct 14 is defined by a stationary lower-lip wall 21 and by an upper-lip wall 22 that pivots around a horizontal articulated joint M. The upper-lip beam and, along with it, the upper-lip wall 22 are arranged to be pivoted by means of a screw gear 23 around said articulated joint M. The profile bar 15, which defines the slice from above, is regulated by means of a series of adjusting spindles 24 and by means of a series of adjusting gears 25. The headbox in accordance with the invention comprises a number of additional-flow pipes 26a 1 , 26a 2 ... as fitted in the direction of width of the headbox and preferably also, when the longitudinal section of the headbox is examined, a number of additional-flow pipes 26a 1.1 , 26a 1.2 , 26a 1.3 ; 26a 2.1 , 26a 2.2 ... 26a 3.1 , 26a 3.2 ... 26a 3.n ... 26 n.1 , 26a n.2 ... 26a n.n as arranged vertically. In the way shown in Fig. 1, in the vertical direction, four additional-flow pipes 26a 1.1 , 26a 1.2 , 26a 1.3 , 26a 1.4 are fitted in each position of width. Said regulation of four additional-flow pipes is arranged to take place as groups R 1 ,R 2 ... An actuator 27a 1 , 27a 2 ... is fitted to displace each group R 1 ,R 2 ... at the same time in the longitudinal direction of the headbox (arrow L 1 ), viewed in the machine direction. Thus, the additional-flow pipes 26 in each group R 1 ,R 2 are displaced at the same time towards the turbulence generator 20, and, however, the group R 1 ,R 2 ... is, at the same time, also brought further apart from the turbulence generator 20. Each additional-flow pipe 26 comprises a regulation device 28, preferably a bushing, by whose means the flow of pulp and/or water in the additional flow is regulated into the additional-flow pipe 26. Each additional-flow pipe 26 is opened at its end into the intermediate chamber 19. Fig. 2 shows the headbox as viewed from above in the direction of the arrow K 1 in Fig. 1. In the headbox, in its different positions of width, a number of additional-flow pipes 26a 1 ,26a 2 ... have been arranged so as to regulate the consistency of the pulp suspension to the desired level at each position of width. In the way shown in the figure, the additional-flow pipes 26a 1 ,26a 2 ... are placed in groups R 1 ,R 2 ... of three pipes so that each group can be regulated by means of an actuator 27a 1 ,27a 2 of its own. The three pipes 26 in each group R 1 ,R 2 are, thus, displaced at the same time into the desired position in relation to the inlet openings C 1 ,C 2 ... of the turbulence tubes 29a 1 ,29a 2 ... at the inlet end of the turbulence generator 20. The closer the pipes 26 in the group R 1 ,R 2 ... are brought to the inlet openings C 1 ,C 2 ... of the turbulence tubes 29a 1 ,29a 2 ... in the turbulence generator 20, the more is the pulp suspension throttled that flows from the intermediate chamber 19 into the turbulence tubes 29a 1 ,29a 2 ... In a corresponding way, when the additional-flow pipes 26a 1 ,26a 2 ... are brought further apart, said throttle is reduced and, thus, the pulp suspension flow Q 1 from the intermediate chamber 19 into the turbulence tubes 29a 1 ,29a 2 ... in the turbulence generator is increased. The consistency of the pulp suspension is regulated by regulating the additional flow Q 2 . In the solution of equipment in accordance with the invention, the bushing 28 can be displaced into different covering positions in relation to the inlet opening A for the additional flow in the additional-flow pipe. Each bushing 28 is operationally connected with the rear wall of the additional-flow chamber 31 preferably by means of a threaded or press fitting N. When the additional-flow pipe 26 is displaced by means of the actuator 27, the bushing 28 remains in its position while there is a glide fitting between the bushing 28 and the additional-flow pipe 26. The area of the inlet opening of the additional flow Q 2 changes so that the sum flow Q 3 = Q 1 + Q 2 remains invariable. The inlet opening A is shaped so that the change in the consistency can be made linear. When the bushing 28 is displaced in relation to the rear wall of the additional-flow chamber, with a certain mixing ratio it is possible to regulate the flow quantity of the sum flow Q 3 . When the additional-flow pipe 26 and the bushing 28 are shifted towards the turbulence tube, the flow quantity of the flow Q 3 is reduced. In a corresponding way, when both the additional-flow pipe 26 and the bushing 28 are brought further apart from the turbulence tube of the turbulence generator 20, the flow quantity of the flow Q 3 is increased. Fig. 3 shows the relative position of the additional-flow pipe 26 and the inlet pipe 29 of the turbulence generator 20 when the inlet pipe 29 of the turbulence generator 20 includes a conical inlet opening C, into whose conical portion C a the end of the additional-flow pipe 26 can be placed. Figure 4 shows a second embodiment of the operational connection between the additional-flow pipe 26 in the headbox in accordance with the invention and the turbulence tube 29 in the turbulence generator, in which embodiment the inlet opening C of the turbulence tube 29 comprises a straight, non-conical end. The operation of the regulation itself is similar both in the embodiment of Fig. 3 and in the embodiment of Fig. 4. Figure 5 shows two different regulation positions of the regulation bushing 28 in relation to the inlet opening A of the additional flow Q 2 in the additional-flow pipe 26. In the way shown by the dashed lines, the bushing 28 has been made to glide on the additional-flow pipe 26 into a position that covers the inlet opening A of the additional flow more fully, and the non-dashed lines show a position in which the bushing 28 is placed fully away from the inlet opening A, in which case the throttle of the additional flow Q 2 is at the minimum. Fig. 6 shows an embodiment in which the operational coupling between the regulation bushing 28 and the additional-flow pipe 26 is accomplished by means of a glide joint 30. Between outer face 28' of the bushing 28 and the through opening 32a in the end wall 32 of the distribution chamber 31 for the additional-flow medium, there is preferably a threaded joint N. Between the intermediate chamber 19 and the distribution chamber 31 for the additional-flow medium, there is a common wall 33, through whose opening 33a the pipe 26 is passed with a glide fitting. Fig. 6 shows the bushing 28 in a position in which the inlet opening A of the additional-flow pipe 26 is fully closed. In the regulations shown in Figs. 7A to 7C, the additional flow Q 2 is water. Fig. 7A shows a first regulation position of the regulation in accordance with the invention, wherein the additional-flow pipe 26 is fitted at the vicinity of the inlet opening C of the turbulence tube 29 in the turbulence generator. Q 3 = Q 1 + Q 2 . The consistency of the flow Q 3 is D 1 . Fig. 7B shows a regulation position in which the additional-flow pipe 26 has been shifted rearwards while the bushing 28 remains in its place. Then, the throttle of the flow Q 2 is increased and, correspondingly, the throttle of the flow Q 1 is reduced by the corresponding amount. The mixing ratio of the sum flow Q 3 = Q 1 + Q 2 is regulated continuously while the flow Q 3 remains at its invariable quantity value. The bringing of the additional-flow pipe 26 apart from the turbulence generator is illustrated by the arrow L 1 '. The consistency of the flow Q 3 is adjusted to D 2 . Fig. 7C illustrates an embodiment of the regulation in which, with the regulated mixing ratio of Fig. 7B and with the consistency D 2 , the flow quantity of the flow Q 3 is supposed to be reduced. In the way shown in Fig. 7C, the additional-flow pipe 26 is placed (arrow L 1 '') close to the mouth opening of the turbulence tube 29 in the turbulence generator. Then, the flow Q 1 is reduced and, to keep the mixing ratio at its regulated value D 2 , the bushing 28 is shifted in the way shown by the arrow L 2 '' into a position of increased covering in relation to the opening A of the additional-flow pipe 26. If the flow quantity of the flow Q 3 is to be increased by means of the mixing ratio of Fig. 7B, the additional-flow pipe 26 is brought further apart from the end of the turbulence tube in the turbulence generator and, correspondingly, the throttle of the flow Q 2 is reduced by moving the bushing 28 in the same shifting direction, whereby the covering of the opening A is reduced.

Claims: Method of regulating a headbox for controlling the grammage profile of a web, the headbox comprising in the flow direction (F) of the pulp suspension an inlet header (17), a distribution manifold (18), an intermediate chamber (19), a turbulence generator (20) comprising a plurality of tubes (29, 29a 1 , 29a 2 ), and a discharge duct (14), in which method additional flows (Q 2 ) are introduced into the pulp suspension at different points across the width of the headbox, the concentration of said additional flows differing from the average concentration of the pulp suspension fed into the intermediate chamber (19), the additional flows being introduced through additional-flow pipes (26, 26a 1 , 26a 2 ) in the vicinity of the inlet openings (C, C 1 , C 2 ) of the tubes (29, 29a 1 , 29a 2 ) of the turbulence generator (20) in the intermediate chamber (19), and in which method the grammage profile of the web in the width direction thereof is regulated by adjusting the distance between the end of the additional-flow pipes (26, 26a 1 , 26a 2 ) and the turbulence generator (20), so that the amount of pulp suspension flowing from the intermediate chamber (19) into the tubes (29, 29a 1 , 29a 2 ) of the turbulence generator (20) is affected, and at the same time adjusting the amount of additional flow (Q 2 ) entering into the additional-flow pipes (26, 26a 1 , 26a 2 ), whereby the concentration of the combined flow (Q 3 ) into the tubes (29, 29a 1 , 29a 2 ) of the turbulence generator (20), which corresponds to the sum flow of the pulp flow (Q 1 ) from the intermediate chamber (19) and the flow (Q 2 ) from the additional-flow pipes (26, 26a 1 , 26a 2 ), is regulated. Method as claimed in claim 1, characterized in that such an additional-flow pipe (26) is used in which the inlet opening (A) is placed in the mantle face of said pipe and fitted to open into an additional-flow distribution chamber (31), from which chamber the additional flow (Q 2 ) is passed into the additional-flow pipe (26), and in that the amount of additional flow (Q 2 ) is regulated by displacing the additional-flow pipe (26) with respect to a bushing (28) placed around the additional-flow pipe (26) so that the inlet opening (A) is differently covered by the bushing (28) during the regulation. Method according to claim 2, characterized in that the flow quantity of the sum flow (Q 3 ) is regulated by displacing the bushing (28). Method as claimed in any of the preceding claims, characterized in that the additional flow (Q 2 ) consists of water. Method as claimed in any of the preceding claims 1 to 3, characterized in that, as the additional flow (Q 2 ), a pulp suspension is used whose concentration differs from the average pulp suspension concentration in the headbox. Method as claimed in any of the preceding claims, characterized in that, in the method, the additional-flow pipes (26a 1 ,26a 2 ...) are grouped as groups (R 1 ,R 2 ...) placed one above the other in different width positions across the headbox of the paper machine, and that in the method the additional-flow pipes (26a 1 ,26a 2 ...) are displaced by means of an actuator (27a 1 ). Method as claimed in any of the preceding claims, characterized in that the additional-flow pipes (26a 1 ,26a 2 ...) are fitted as groups (R 1 ,R 2 ...) in the direction of width of the headbox, each group (R 1 ,R 2 ...) being displaced (arrow L 1 ) by means of an actuator (27a 1 ) of its own. Headbox comprising in the flow direction (F) of the pulp suspension an inlet header (17), a distribution manifold (18), an intermediate chamber (19), a turbulence generator (20) comprising a plurality of tubes (29, 29a 1 , 29a 2 ), and a discharge duct (14), the headbox further comprising additional-flow pipes (26, 26a 1 , 26a 2 ) fitted in different width positions across the width of the headbox for introducing additional flows (Q 2 ) in the pulp suspension in the vicinity of the inlet openings (C, C 1 , C 2 ) of the tubes (29, 29a 1 , 29a 2 ) of the turbulence generator (20) in the intermediate chamber (19), the concentration of said additional flows differing from the average concentration of the pulp suspension fed into the intermediate chamber (19), the headbox being provided with regulation devices (28) by whose means the additional flow (Q 2 ) into the additional-flow pipes (26, 26a 1 , 26a 2 ) is regulated, characterized in that said additional-flow pipes (26, 26a 1 , 26a 2 ) are fitted to be displaceable towards and away from the tubes (29, 29a 1 , 29a 2 ) of the turbulence generator (20) by means of an actuator (27a 1 ). Headbox as claimed in the preceding claim, characterized in that the additional-flow pipe (26) is provided with an inlet opening (A) placed in the mantle face of said pipe and fitted to open into an additional-flow distribution chamber (31), from which chamber the additional flow (Q 2 ) is passed into the additional-flow pipe (26) and that the regulation device comprises a bushing (28) placed around the additional-flow pipe (26), the additional-flow pipe (26) being displaceable with respect to the bushing (28) to effect different covering positions of the inlet opening (A) by the bushing (28), whereby the amount of additional flow (Q 2 ) into the additional-flow pipe (26) can be regulated. Headbox as claimed in claim 9, characterized in that the bushing (28) is fitted in an end wall (31a) of the distribution chamber (31) and in that a press fitting or a threaded joint (N) is provided between the bushing (28) and said end wall (32). Headbox as claimed in claim 9, characterized in that a glide fitting is provided between the bushing (28) and the additional-flow pipe (26). Headbox as claimed in claim 11, characterized in that, when the end of the additional-flow pipe (26) is displaced by means of the actuator (27a 1 ) into different distances from the tube (29) of the turbulence generator (20), the bushing (28) remains in its position and, when the amount of flow (Q 1 ) from the intermediate chamber (19) into the tube (29) of the turbulence generator (20) is reduced, the amount of additional flow (Q 2 ) from the additional-flow pipe (26) is increased to a corresponding extent, and the other way round. Headbox as claimed in any of the preceding claims 8 to 12, characterized in that the additional-flow pipes (26a 1 ,26a 2 ...) are interconnected as groups (R 1 ,R 2 ...), which are displaced by means of actuators of their own (27a 1 ). Headbox as claimed in any of the preceding claims 8 to 13, characterized in that the additional-flow pipe (26) is placed centrally in relation to the turbulence tube (29) of the turbulence generator and so that the central axis (X 1 ) of the turbulence tube and the central axis (X 2 ) of the additional-flow pipe are placed on the same straight line. Headbox as claimed in any of the preceding claims 8 to 14, characterized in that the inlet opening (C) of the turbulence tube (29) of the turbulence generator comprises a conical widening, into which the end of the additional-flow pipe (26) can be placed. Headbox as claimed in any of the preceding claims 9 to 15, characterized in that the distribution chamber (31) is formed directly in connection with the intermediate chamber (19), the chambers comprising a common partition wall (33). Headbox as claimed in any of the preceding claim 16, character i z e d in that each additional-flow pipe (26a 1 ,26a 2 ...) is fitted to pass from the intermediate chamber (19) through the common wall (33) of the intermediate chamber (19) and distribution chamber (31) and through said distribution chamber (31), and that the actuator (27a 1 ) is fitted to engage with the end of the additional-flow pipe (26) to displace the additional-flow pipe towards or away from the turbulence generator (20).

Inventors: PITKAEJAERVI KARI, PITKAEJAERVI, KARI, Pitkäjärvi, Kari
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1994
Main classification: D21F1
IPC codes: D21F1